The residue from alkali refining of fats is generally referred to as "raw soapstock". It is raw soapstock which is the product which is treated by the method of the present invention to provide a fluid, pumpable animal feed product which is also resistant to microbiological and chemical degradation. Raw soapstock is a thick, viscous material which is difficult to pump and which is subject to rapid deterioration by microbiological and chemical degradation. The present invention is directed to a method for making soapstocks more fluid and easily pumpable.
Animal fats and oils consist of triglycerides which are esters of glycerol and fatty acids. Because the fatty acid radical constitutes the greater part of the glyceride molecule, and also the reactive portion, the chemical and physical properties of a fat or oil are determined largely by the properties of the component fatty acids. In general, fats become progressively higher melting and more easily solidified as the average molecular weight of the fatty acid increases, and as their average unsaturation decreases. There is no rigid distinction between "oils" which are liquid at ambient temperature and "fats", which are solid or semi-solid at ambient temperature. For simplicity, the term "fat" is used herein in referring to either the liquid or solid forms of edible triglycerides.
The crude fat, as obtained from a pressing or solvent extraction operation contains impurities which are removed by refining the crude fat. One of the more prevalent impurities is in the form of free fatty acids. Free fatty acids are most often removed from the crude fat by alkali refining. Alkali refining is generally carried out by treating the fat with a strong solution of caustic soda. The process involves emulsifying the fat with a considerable excess of an aqueous solution to saponify the fatty acids and form a soap, heating to break the emulsion, and separation of the refined fat from the precipitated soap and miscellaneous associated impurities. A small proportion of the triglycerides are also saponified in addition to the reaction of the caustic soda with the free fatty acids. The precipitated material removed from the refined oil is known in the trade as "soapstock".
Soapstock generally contains from about 30% to about 50% of fatty acids, from about 25% to about 60% of moisture and from about 3% to about 12% of nonfatty components, including gums, such as lecithin. Soapstock has been used in soap making and the manufacture of commercial fatty acids. More recently, however, because of the high energy value of soapstock, soapstock has been used as a feed supplement in finished feed formulations for animals.
It is known to reduce the amount of moisture in soapstock to prevent microbiological and chemical degradation. One of the most commonly used methods for reducing the moisture of soapstock is by acidulation. Acidulation is accomplished by boiling the soapstock in an open tank or kettle with sulfuric acid, using open steam for heating and agitation. The acid must be used in considerable excess. After about 2-4 hours of vigorous boiling, the charge is allowed to settle for a short time and the fatty layer is tested for total fatty acid content. If the fatty acid content is satisfactory, settling is continued overnight or for a minimum of about 4-6 hours. If the total fatty acid is low, additional acid is added and boiling and settling are repeated. After the addition of acid is completed and the charge is well settled, the lower water and mineral acid layer, plus a certain amount of sludge is discharged. The fatty material is then washed by adding 1/4 to 1/2 its own weight of water, followed by boiling for a short time, settling overnight and discharging the wash water. One wash is usually sufficient to reduce the mineral acid content sufficiently to obtain a substantially neutral pH. Thus, the low moisture fatty acid product recovered from the acidulation process is not itself at an acid pH.
Accordingly, it is a principal object of the present invention to provide a method for treatment of a fat containing a substantial level of free fatty acids, gums and moisture to provide a fluid pumpable product.
It is another object of the present invention to provide a method for treatment of raw soapstock to provide a fluid, pumpable animal feed product.
It is a further object of the present invention to provide an animal feed product which contains a high level of energy and which can contribute to the preservation of a finished feed formulation.
These and other objects of the invention will become more apparent from the following description and the depended claims.